Interchangeable biosimilars cut drug spend only when pharmacies can actually switch them

Interchangeability has stopped being a novelty. It’s becoming a lever that pharmacy and payer ops teams can actually pull, but only if their switching, claims, and inventory systems are built to handle it.

The latest signal is category breadth. In October 2023, the U.S. Food and Drug Administration approved Amgen’s Wezlana (ustekinumab-auub) as a biosimilar to and interchangeable with Janssen’s Stelara (ustekinumab) across multiple inflammatory indications, including Crohn’s disease and ulcerative colitis, according to Healthcare Purchasing News. In September 2026, a Drug Watch item in the American Journal of Nursing (AJN), accessed via Ovid, reported the FDA approved golimumab-sldi as the first interchangeable biosimilar to golimumab for severely active rheumatoid arthritis (in combination with methotrexate) and moderately to severely active ulcerative colitis.

The operational point: interchangeability changes who has to decide, and when

A standard biosimilar decision often lands with P&T committees, specialty pharmacy, prior authorization, and prescriber education. Interchangeability shifts some of that decision-making downstream to dispensing, because the FDA designation enables pharmacy-level substitution without contacting the prescriber, although state pharmacy laws still control the exact mechanics, as both Healthcare Purchasing News and Managed Healthcare Executive note in their coverage of FDA explanations.

That difference sounds legalistic until it hits the shop floor. For hospital pharmacies and health-system outpatient pharmacies, it affects how substitution logic is configured in dispensing software, how e-prescribing messages are interpreted, and how staff handle patient notification and prescriber “dispense as written” signals where state rules require them. For payers and PBMs, it shows up as NDC-level adjudication, step edits, and formulary messaging that must align with what dispensing channels can do in practice.

Insulin showed the pattern, and the numbers were not subtle

The best real-world clue that interchangeability is more than a label comes from insulin. Managed Healthcare Executive reported in July 2021 that the FDA approved Semglee (insulin glargine-yfgn) as both biosimilar to and interchangeable with Sanofi’s Lantus, and that pharmacists could substitute it subject to state rules. The same piece noted the FDA had approved 29 biosimilars at the time, and Semglee was the first interchangeable biosimilar insulin product.

Podiatry Today, citing an economic evaluation by Murphy and Holtkamp in JAMA Health Forum (published May 2, 2025), described what happened next. Using IQVIA National Prescription Audit and PayerTrak data from September 2019 through June 2024, the researchers applied interrupted time-series methods and found a step-change increase in biosimilar dispensing immediately after the FDA granted interchangeability in November 2021. In Podiatry Today’s summary, Semglee and insulin glargine-yfgn together increased by more than 47,000 prescriptions right after that designation.

Two implementation details in that analysis matter to operators. First, Podiatry Today reports the increase occurred across retail, mail order, and long-term care pharmacy channels, suggesting interchangeability can carry across multiple dispensing workflows instead of being confined to one setting. Second, in payer-specific results, the study reported especially strong uptake of insulin glargine-yfgn among Medicare Part D, Medicaid, and cash-paying patients, which suggests the designation is most visible where out-of-pocket sensitivity is highest.

Wezlana and golimumab raise the stakes for specialty and clinic-adjacent spend

Ustekinumab and golimumab are different operational animals than insulin glargine. They touch specialty distribution, cold-chain handling, and, depending on care setting, clinic workflows and patient support programs. Still, the FDA’s stance on interchangeability is consistent: Healthcare Purchasing News reported that the agency’s approval of Wezlana was based on a comprehensive review intended to show high similarity to Stelara and no clinically meaningful differences in safety, purity, and potency, along with evidence to meet the additional legal requirements for interchangeability.

The AJN Drug Watch item accessed via Ovid is short, but the timing is the news. A September 2026 report of an interchangeable biosimilar to golimumab suggests interchangeability is extending further into immunology categories where utilization management has traditionally leaned on prescribers, specialty pharmacies, and infusion site-of-care controls.

For procurement and pharmacy buyers, that broadening matters in a practical way: the first quarter after a switch is when bins, labels, and order sets get messy. Interchangeability can reduce prescriber touchpoints, but it increases the importance of clean product master data, barcoding practices, and contract language that makes the “preferred” product operationally preferred, not just financially preferred.

Where pharmacy directors and payer ops teams should pressure-test their setup now

• Map state substitution requirements to your actual dispensing footprint. Interchangeability is federal, substitution rules are state-by-state, and both Healthcare Purchasing News and Managed Healthcare Executive emphasize that variability. Multi-state systems need a rule table, not a memo.
• Audit your NDC and product mapping for interchangeable pairs before you add a new preferred agent. The insulin evidence base described by Podiatry Today suggests utilization can jump quickly after designation. If claims edits or dispensing catalogs lag, the first month will be noisy.
• Decide how prescriber intent will be captured and honored. If “dispense as written” logic is inconsistently represented across eRx, EHR, and pharmacy systems, substitution will become exception handling.
• Put inventory and cold-chain handling in the same meeting as formulary and contracting. Ustekinumab-class products can stress storage and replenishment patterns in a way insulin did not, and operational readiness is what makes a switch stick.